1. Field of the Invention
The present invention relates generally to systems and methods for characterizing, synthesizing, and/or canceling out acoustic signals from inanimate sound sources, and more particularly for using electromagnetic and acoustic sensors to perform such tasks.
2. Discussion of Background Art
Sound characterization, simulation, and cancellation are very important ongoing fields of research and commercial practice. Inanimate sound sources range from pleasant sounding musical instruments to very harsh and possibly harmful sounds from engines, air ducts, machines, and/or heavy equipment. Modern recording systems analyze and characterize inanimate sound sources, synthesizers use this characterized data to attempt to mimic various musical instruments, and noise cancellation technology uses prior analyzed data to reduce undesired sound levels.
Two prior art methods are in use today for analyzing and synthesizing sounds. The first method records long time duration segments of a sound, then divides them into shorter xe2x80x9csegments.xe2x80x9d During synthesis, the segments are arranged and concatenated as needed to synthesize a desired sound sequence. Such methods are often used to simulate musical instruments, as described in U.S. Pat. No. 5,111,727 entitled, xe2x80x9cDigital sampling instrument for digital audio dataxe2x80x9d by D. P. Rossum. The second method of sound analysis and synthesis involves using measured or simulated sound system elements, such as sine waves, which are processed and modified for play back as desired. A prior art analog system of this nature is described in U.S. Pat. No. 4,018,121 entitled, xe2x80x9cMethod of synthesizing a musical soundxe2x80x9d by J. M. Chowning. However, a shortcoming of these two prior art methods is that they do not use excitation source information to analyze, synthesize, and cancel sounds that inanimate objects make.
FIG. 1 is a dataflow diagram of a third prior art sound analysis and synthesis system. The third system is typical of those currently used in digital musical synthesizers and is further described in U.S. Pat. No. 5,029,509 entitled, xe2x80x9cMusical synthesizer combining deterministic and stochastic waveformsxe2x80x9d by X. Serra and J. Smith. To begin, a sound signal 102 is recorded from an acoustic microphone. In step 104, a time frame is set and a fundamental pitch is determined for the sound signal 102, in step 106. Next in step 108, one or more sine wave functions are generated with the same time frame and harmonic relationships as the sound signal 102. The sine functions are fitted, in step 109, to the sound signal 102 and, in step 110, a corresponding set of amplitudes, phases, and frequencies for the sine functions are stored in memory 112. The sine functions, best fit by one or more harmonic waves, are then subtracted from the sound signal 102 to generate a residual acoustic signal 114. The residual signal 114 is then fitted 116 to a white noise signal from a white noise generator 118. The white noise signal can be further characterized using a Linear Predictive Coding (LPC) technique, also called an all-pole method technique. Next in step 120, coefficients that fit the noise signal to the residual signal 114 are stored in the memory 112 and are recalled on command.
As a first step in synthesizing the sound signal 102, MIDI or other sound control systems call for the needed sequence of amplitude, pitch, attack, reverberation, and other control variables 122. Next, in step 126, the coefficients stored in the memory in step 120 that describe the sine and residuals are modified to generate variations of the stored sounds, according to the user""s control description. In step 128, sequences of sine functions describing the harmonic aspects of the desired synthesized signal are added together. The functions describing the residual signal 114 are added to the summed harmonic functions to make a single time frame of a sound sequence signal 130. Finally, sequential frames are added together to make a multiframe sound sequence signal 130, which is then amplified through a speaker 132 for a listener 134 to hear. Ideally the multiframe sound sequence signal 130 is as close a match as possible to the original sound signal 102.
A variant on the third prior art method is described in U.S. Pat. No. 5,587,548 entitled, xe2x80x9cMusical Tone Synthesis System Having Shortened Excitation Table,xe2x80x9d by Smith. Smith describes how to use previously measured sound excitations, usually obtained by impulsive excitation of body modes, to synthesize a musical sound. In addition, Smith uses computed xe2x80x9cloopsxe2x80x9d whose cycle rate defines pitch values for synthesized sound. This process is called xe2x80x9cphysical modeling synthesis.xe2x80x9d This process often uses simplified functional descriptions of vibrating mechanical elements to describe the mechanics of string motions, their coupling to the body via a bridge, and to resonator panels in musical instruments.
None of these prior art methods accurately captures qualities of inanimate sound sources because they are only based upon approximating an output signal, or intermediate process, and fail to accurately characterize the underlying physical processes of sound generation and their collective behavior. Such methods also have difficulty defining time frames based upon a natural cycle of the sound sources, and in forming accurate transfer functions and associated filters, especially in high noise environment. As a result, prior art methods are not able to accurately synthesize well-known musical instruments, such as Steinway pianos, Stradivarius violins, ebony clarinets, and other fine instruments to the degree desired. In addition, these prior art analysis methods tend to not work well in real time sound cancellation applications.
Separate from the three methods described above, hybrid sound generators, such as are used in electric guitars, generate sounds by monitoring excitation sources, such as strings on a musical instrument. In these hybrid instruments, acoustic sounds from the musical instrument itself are usually ignored. U.S. Pat. No. 5,572,791 entitled, xe2x80x9cMethod for positioning a pickup on an electric guitarxe2x80x9d by K. Kazushige and U.S. Pat. No. 4,321,852 entitled, xe2x80x9cStringed instrument synthesizer apparatusxe2x80x9d by L. D. Young Jr. describes these techniques and methods in more detail. As a result, typical guitar string sensors only measure approximate excitations of the musical instrument, which are then fed to an amplifier, filter bank, and loud speaker.
The prior art methods of sound analysis and synthesis are also applied to the problem of canceling out undesirable sounds. These methods are described in references such as the Encyclopedia of Acoustics, Vols. I-IV, M. J. Crocker ed., Wiley, N.Y. 1997; Vol. II chapters 79-89 and Vol. IV chapters 130-139, in U.S. Pat. No. 5,517,571 entitled, xe2x80x9cActive noise attenuating device of the adaptive control typexe2x80x9d by S. Saruta and Y. Sekiguchi, and also in U.S. Pat. No. 5,448,645 entitled, xe2x80x9cActive fan blade noise cancellation systemxe2x80x9d by J. R. Guerci. Each of these sound cancellation methods, however, is incapable of rapidly and economically analyzing and canceling out the undesirable sounds to the degree needed, especially for rapidly changing (e.g., chaotic) sounds.
In practice, obtaining accurate mathematical functions of complex sound systems is currently very difficult. Prior art excitation transducers are not accurate or fast enough and prior art algorithms are restricted to using LPC methods. Furthermore, digital processors are too slow and expensive to handle needed information, and required memories are costly. As a result, automating sound analysis so that a wide variation in sound inputs can be automatically analyzed and stored in memory for subsequent synthesis, especially in xe2x80x9creal time,xe2x80x9d is very difficult, if not impossible in some cases. There is a need in the art for more accurate systems, for faster systems, and methods for more accurately characterizing, synthesizing, and/or canceling out acoustic signals from inanimate sound sources.
In response to the concerns discussed above, what is needed is a system and method for characterizing, synthesizing, and/or canceling out acoustic signals from inanimate sound sources that overcomes the problems of the prior art.
The present invention is a system and method for characterizing, simulating, and/or canceling out acoustic signals from inanimate sound sources. An overall method for characterizing an inanimate sound source includes the steps of generating a numerical excitation function from excitations of the inanimate sound source; generating a numerical acoustic function from acoustic emissions of the inanimate sound source; and deconvolving the excitation function from the acoustic function to generate a transfer function which characterizes the inanimate sound source. An overall method for synthesizing acoustic signals representing an inanimate sound source includes the steps of: receiving synthesis instructions; retrieving an excitation function from a memory based on the synthesis instructions; retrieving a transfer function from the memory based on the synthesis instructions; and convolving the excitation function with the transfer function to synthesize an acoustic signal. An overall method for canceling out acoustic signals from an inanimate sound source includes the steps of: instantly generating an excitation function from excitations of the inanimate sound source; instantly generating an acoustic function from acoustic emissions of the inanimate sound source; calculating and storing in memory a transfer function from the excitation function and the acoustic function; receiving cancellation instructions; convolving the excitation function with the stored transfer function to synthesize a canceling acoustic signal; and broadcasting the canceling acoustic signal proximate to the acoustic emissions and fast enough to effect cancellation.
A system for characterizing acoustic signals from an inanimate sound source, includes an electromagnetic (EM) sensor for monitoring excitations from the inanimate sound source; an acoustic sensor for monitoring acoustic emissions from the inanimate sound source; an EM processor for converting the excitations into an excitation function; an acoustic processor for converting the acoustic emissions into an acoustic function; a transfer function processor for generating a transfer function from the excitation function and the acoustic function. Additional EM sensors may be used to monitor secondary excitations and for generating additional transfer functions which characterize the inanimate sound source.
A system for synthesizing acoustic signals from an inanimate sound source, including a memory containing an excitation function and a transfer function; a synthesis control unit for generating synthesis instructions; and a synthesis processor for retrieving the excitation function and the transfer function, and convolving the excitation function with the transfer function to synthesize an acoustic signal.
A system for canceling out acoustic signals from an inanimate sound source, including an electromagnetic processor for instantly generating an excitation function from excitations of the inanimate sound source; an acoustic processor for instantly generating an acoustic function from acoustic emissions of the inanimate sound source; a transfer function processor for calculating and storing a transfer function from the excitation function and the acoustic function; a synthesis processor for receiving cancellation instructions, and for convolving the excitation function with the stored transfer function to synthesize a canceling acoustic signal; and a broadcasting unit for broadcasting the canceling acoustic signal proximate to the acoustic emissions.
While the present invention is particularly applicable to repetitive and well-defined excitation sources, such as musical instruments, non-periodic excitation sources, such as windowpanes, automobile road noise, air duct noise can also be analyzed, synthesized, or canceled out when modeled as including one or more excitation sources. Important applications of the present invention include noise cancellation in rooms or automobiles, and chaotic sound generation such as is typical of rattles, and drum snares. The present invention also finds application to musical synthesizers, sound effects generators, and video and movie sound synchronization.
These and other aspects of the invention will be recognized by those skilled in the art upon review of the detailed description, drawings, and claims set forth below.